Figure 1

Osmium isotope values, generic diversity and palaeogeography in the Late Triassic.

(a) Late Triassic generic diversities of radiolarians²³, conodonts⁴¹ and Pacific (North American) ammonoids⁴⁰, as compared with the Os isotope record^9,45 in the Panthalassa Ocean. The abrupt decrease in the ¹⁸⁷Os/¹⁸⁸Os ratio in the middle Norian is synchronous with the Manicouagan impact event at 214–215 Ma. Stepwise or episodic extinctions in the (1) end-middle Norian, (2) end-Norian and (3) end-Triassic are possibly linked with a large bolide impact⁷, an oceanic anoxic event (OAE)⁴ and the Central Atlantic Magmatic Province (CAMP) volcanic event^5,6, respectively. The gradual decrease in radiolarian diversity just prior to the end-middle Norian may have occurred within radiolarian biozone 6B. Gray shaded areas in the radiolarian and conodont generic diversities represent the number of genera; the genera first appear in the upper Norian and Rhaetian. The geological time scale is from refs 46 and 47. Triassic radiolarian fossil zones (FZ) and their age correlations are from refs 7, 20 and 48; the biostratigraphic framework for our age model is shown in Supplementary Fig. S2. (b) Late Triassic palaeogeographic map showing approximate locations of the Manicouagan carter and the inferred depositional area of the bedded chert in the Mino Belt, in low-latitude zones of the Panthalassa Ocean¹¹. The map is created using ACD Systems Canvas Draw software (Version 2.0).